Producing an inexpensive yet effective water filtering apparatus has been the goal of many workers. One such early attempt utilizing a filter apparatus threadably attachable to one bottle and into which a second bottle may be inserted is taught by U.S. Pat. No. 2,167,225 to Van Eweyk. The water filtering apparatus taught by Van Eweyk comprises a cylindrical apparatus having a threaded aperture at one end for threadably attaching to a bottle or similar container. The upper end of the filtering apparatus of Van Eweyk is open, whereby the neck of a second bottle may be received therein, the second bottle being retained in the apparatus by gravity. The apparatus contains a quantity of water purifying media through which water passing from the second or upper bottle flows through the media and thence into the lower or first bottle.
A somewhat similar device is disclosed in U.S. Pat. No. 5,240,620 to Shalev. Shalev teaches an apparatus for filtering water comprising an enclosure containing a quantity of filter media. The enclosure of Shalev is fitted with an entrance and an exit spout, at least one of which is dimensioned to be received into the neck of a receiving container such as a bottle. In use, the filtering apparatus of Shalev has its entrance spout inserted into an upright bottle of water and a second bottle is placed over the exit spout. A user then holds the filter between the two bottles while inverting them, and gravity urges water from the first bottle into the second. Shalev recognizes the likelihood of water spillage from such a device and therefore provides a damn or buffer to receive water excess to the filtration process.
Neither the device of Shalev nor of Van Eweyk recognizes the importance of providing a dedicated air passage to ensure passage of displaced air from the lower container to the upper container. Such an air passage or vent will serve to ensure an efficient and timely transfer of water from the upper container to the lower. U.S. Pat. Nos. 4,749,484 and 4,978,449 make such provision.
The '484 patent to Greenhut teaches a filter apparatus for insertion into a two-chambered container wherein the chambers of the container are positioned one atop the other. As water flows under gravity through the filter, air is displaced from the lower chamber to the upper. In order to ensure the free passage of this air, Greenhut teaches two methodologies. First, Greenhut does not position a preliminary filter directly on top of his primary filter material, maintaining that bubbles formed during the filtering process could block the flow of water through the primary filter in an unpredictable manner. Secondarily, Greenhut provides a secondary vent having a lower end opening into the top of the lower vessel thereby receiving air displaced during filtration. This vent tube has an upper end defining a hole near the upper end of the upper vessel for venting air therein.
The '449 patent to Devine et al. is a further improvement to the filter apparatus taught by Greenhut. Devine et al. teach a single air vent positioned above the mass of filter media, the vent having a retainer therein which allows air to pass up through the air passage or vent while limiting, but not eliminating, movement of the filter material out of the housing should the water filter be inverted.
Both the Van Eweyk and Shalev patents rely on gravity to maintain the bottles and filter in their relative positions during use. It will be immediately apparent therefore that any disturbance of this apparatus, or substantial blockage of the filter would likely lead to significant spillage. In order to optimally improve the taste of municipally treated water and to improve its safety after transport in metallic pipes, particularly soldered pipes, a filtering system having two active filter elements is preferred. The combination of activated carbon to reduce chlorine as well as other off tastes and odors, and a cationic exchange resin to remove lead and other heavy metals has proven particularly advantageous. This fact is recognized by the teachings of Devine et al. who further point out the desirability of not admixing large amounts of the ion exchange material with the relatively fine carbon grains.
In order to minimize the admixture of filter media during shipment, while enabling a reasonably efficient transfer of air from the lower bottle to the upper, Devine et al. teach an air space above the ion exchange material at the top of which is a water and air permeable retainer. The retainer keeps the ion exchange material in the filter apparatus, and limits but does not eliminate the movement and hence the admixture of the two active elements. The air space above the ion exchange material is necessary in the apparatus of Devine et al. in order to allow the upward flow of air to start and then to continue as water flows through the filter. Without such an air space formed by the air passage, the first quantity of air released from the water flowing through the filter creates an air pressure which prevents further flow of water through the filter.
What is needed is a low-cost, efficient water filtration unit which is securely attachable to, and which seals to two containers to eliminate or significantly reduce water spillage during use. In order to make such a filtration unit efficient, two obstacles must be overcome. First, a methodology must be found to enable the orderly transfer of water from the upper container to the lower, and the concomitant simultaneous transfer of air from the lower to the upper. Second, a methodology must be found for preventing the admixture of the active filtration elements during the repeated inversions occasioned by the use of such a filtration unit.